In-band credit management allows credits to be incrementally granted
with each PPP Session Stage packet. These in-band incremental credit
| grants are not explicitly unacknowledged. However, they are
reflected in the in-band credit flow from the peer node.

It should say:

In-band credit management allows credits to be incrementally granted
with each PPP Session Stage packet. These in-band incremental credit
| grants are not explicitly acknowledged. However, they are reflected
in the in-band credit flow from the peer node.

Notes:

I strongly suspect that in the second sentence,
"not explicitly unacknowledged"
is an erroneous double negation and should be
"not explicitly acknowledged" .